appropriate controls for DAT+ patients when phenotyping

[Jessi Tobal]

If I have a patient that is DAT+ and I need to do a phenotype. The manufacturers of antisera state that we need to run "appropriate controls" should the DAT be positive. How would I manage that?

[Malcolm Needs ☆]

In the case of most, if not all, monoclonal IgM grouping reagents, you should be able to use your normal controls, unless the auto-antibody reacts at the same temperature as that recommended for the incubation of the grouping reagents.

In the case of IgG antibodies, whether monoclonal or polyclonal, the chances are that you will not get true negative reactions (unless of course, the DAT is caused by a "cold-reacting" antibody of narrow thermal range, and only involves a C3d or IgM and C3d coating, and as long as the incubation is at 37oC).

You could try coating some red cells with a known IgG antibody to use as positive/negative controls.

Lastly, you could try treating the patient's red cells with dithiothreitol (DTT) or ZZAP, but have a care, as some antigens are sensitive to this and are destroyed. It is worth looking in The Blood Group ANtigen FactsBook by Marion Reid and Christine Lomas-Francis, 2nd edition, Elsevier Academic Press, 2004 (ISBN: 0-12-586585-6, Library of Congress Catalog Number 2003102995) for a list of such antigens - it's a fabulous book!

I'm sure other people will have other ideas, but I hope this is of some help.